The present invention relates generally to communication systems, and more specifically the invention pertains to an information acquisition system which controls a tunable radio receiver, with a control algorithm that mimics a human operator, to decode and store digital information received by radio.
Many users of the radio frequency spectrum transmit digitally coded information. Examples of digitally-coded information include Teletype (R), telex, SITOR, AMTOR, packet radio, and telegraphy. The form of modulation employed for all these data transmission modes (except for telegraphy) is binary frequency-shift keying (FSK). FSK is a serial data transmission process in which individual data words are binary-coded as sequences of 1's and 0's. To transmit such a code, the binary 1's are translated to a burst of radio energy at what is called the "mark" frequency, and binary 0's are translated to a burst at a different frequency called the "space" frequency. Bits are sent sequentially. The duration of each burst determines the bit rate: the shorter the burst, the higher the bit rate.
The task of automating the process of scanning a range of radio frequencies in search of Frequency Shift Keying (FSK) signals, and identifying, decoding and storing such signals once they are found is alleviated, to some extent, by the systems disclosed in the following U.S. Patents, the disclosures of which are specifically incorporated herein by reference;
U.S. Pat. No. 4,119,964 issued to Johannsen et al;
U.S. Pat. No. 4,476,535 issued to Loshing et al;
U.S. Pat. No. 4,614,945 issued to Bunius et al;
U.S. Pat. No. 4,704,725 issued to Harvly et al;
U.S. Pat. No. 4,787,063 issued to Muguet; and
U.S. Pat. No. 4,821,122 issued to Teskey.
The above-cited patents include systems which scan a pre-set range of frequencies, and which collect data when a signal is located. Each of these references are discussed below.
The Johannsen et al. reference discloses a radio frequency interference detection system which scans a range of frequencies (3.7-4.2 GHz) stops scanning when locating a signal, and records the angle and amplitude of the signal in a digital format on a computer. While the Johanssen et al. reference is exemplary, the present invention identifies and decodes a message in an information signal (rather than an interference signal) and provides an original controlling software algorithm.
The Loshing et al. reference discloses a system for scanning, monitoring and recording radio frequency signals from different locations. The information is stored in a digital format on a computer memory. The present invention includes an automatically self-adjusting tuneable radio receiver which scans a range of frequencies as controlled by a special computer algorithm. These features are not found in the Loshing et al reference
The Brunius et al. reference disclose a radio frequency scanning and recording system with transponders that receive and transmit messages over a predetermined RF transmission bandwidth. However the frequencies are varied in accordance with a predetermined function in time, and the patented system does not have the scanning and lock-on features and the controlling software of the present invention.
The Harvey and Teskey systems scan multi-channel radio and television signals broadcasts at predetermined frequencies. The Muguet reference receives and records radio and television signal broadcasts. These three references do not have the flexibility to scan the variety and range of frequencies in the manner as the tunable radio frequency receiver of the present invention. While the above-cited references are instructive, a need remains to provide an automatic information acquisition system which mimics a human operator by scanning radio frequencies for FSK signals to identify decode and digitally store them. The present invention is intended to satisfy that need.